It is often desirable or necessary to measure the displacement of the suspended part of a compliance device relative to the fixed portion of the compliance device, such as is often desired with respect to remote center compliance (RCC) devices.
Remote center compliance (RCC) devices, which are passively compliant, are available for assembly, mating and insertion tasks where it is desired to quickly and easily accommodate for relatively small misalignments. Four different types of RCC devices are disclosed in U.S. Pat. Nos. 4,098,001, 4,155,169, application Ser. No. 140,768, filed Apr. 16, 1980, and application Ser. No. 312,513, filed Oct. 16, 1981, incorporated herein by reference. These devices have now been instrumented, so that, as well as passively adjust to assemble misaligned parts, they now are also able to indicate a measure of the misalignment.
Displacements of interest include translational displacements .DELTA.X, .DELTA.Y, of the operator member along two mutually perpendicular axes x, y, which are also perpendicular to the axis of the operator member, and rotational displacement .DELTA..theta..sub.x, .DELTA..theta..sub.y, about the x and y axes.
One technique for the instrumentation of RCC devices for displacement measurement is disclosed in U.S. patent application Ser. Nos. 76,906 and 76,907, filed Sept. 19, 1979, incorporated herein by reference. In such an approach, portions of the detector circuits are mounted on the suspended part, which may include an operator member, and thus are subject to shock loads encountered by the suspended part. Further, the wires or other connection devices used to interconnect the detector circuits on the suspended part with external components must be light and flexible and carefully routed and mounted to avoid interference with the RCC device. Such connection means are subject to breakage and fatique because of the motion of the parts. Separately, since the displacements to be measured are often quite small and there is no mechanical advantage or amplification available inherent in the structure, all of the substantial required amplification must be provided from electronic amplification.
In addition, in such contemporary solutions a coordinate transformation is used which involves sums or differences of the output of the detectors for each desired output, e.g. .DELTA..theta..sub.x, .DELTA..theta..sub.y, .DELTA.X, .DELTA.Y. This transformation combined with the discrete nature of the individual detectors results in relatively low angular and displacement resolution.